Recently, as the VLSI semiconductor manufacture technology and ultra high vacuum technology are rapidly being developed, the search for a triode device having a micron size which has new formation is becoming active. And the flat panel display is observed to develope a new flat display which has merits of CRT and LCD by applying the device to the display device.
FED is a type of a flat display, which emits cold electrons by applying relatively low voltage, for example about 200.about.10 kV using a phenomenon in which electric field concentrates in the edge portion of the screen. FED is formed using the phenomenon has both the merits of high definition of CRT and the thin property of LCD, so it is observed as a display of the next generation.
The FED constitutes cathode of a tip form or wedge form which emits electrons and anode which is deposited with fluorescent material. It guides the emission of an electron from a number of micro tips, and displays a desired picture using light generated in the process in which the most outer electrons are excited and are in transition when the fluorescent material is stimulated.
That is, in FED, electrons emit out of a vacuum from the solid state through tunnelling of quantum mechanics if electric field is applied to the metal or conductor in the vacuum, and they are accelerated by the voltage applied to the electrode behind the opposite side and impinge on the fluorescent layer formed on the electrode to emit light. This is a display device to display image.
The FED not only can be thinly manufactured but can solve the faults of LCD: the process yield, unit price of production and large size of LCD. That is, LCD has the property that the entire product becomes spoiled even if there is fault in one unit pixel. However, since the FET has a number of smaller unit pixels in one group of pixel, there is not a problem in the operation of pixel group even if there are defects in one or two unit pixels. Therefore, the yield of an entire product increases.
Moreover, FED has superior properties to that of the LCD, that is, visual field angle, luminance, speed of response and power consumption. So FED is suitable for a large display device.
An early FED consists of conical emitters which are exposed to the exterior by a cavity and has an edge portion, gates which are lined up in both sides of the emitter and anodes which are parted from the gates in a fixed gap, and where each of them corresponds to the cathode, grid and anode of CRT.
The FED emits electrons using the electric field concentrated in the edge portion of the anode by applying the voltage to the emitter, and the emitted electrons are guided by the anode to which a positive voltage is applied and make the fluorescent covered on the anode emit. In additon, the gates control the direction and quantity of electrons.
The FED has a spacer in order to maintain a fixed gap between upper panel and lower panel.
The spacer is a structure which protects the substrate from being destroyed or bended by the pressure stress due to the high vacuum in the FED and maintains the upper and lower panels in the gap of 100.about.3000 .mu.m conventionally.
The FED needs to have a gap between substrates, where the gap is more than 1 mm for a panel of high luminance and the high emission efficiency although the gap of substrate is in the range of 100.about.3000 .mu.m. However, to make the height of spacer for FED to about 2000 .mu.m, there has been many problems technically, so many formation methods of spacer to solve those problems are being raised.
In the conventional methods to form such a spacer, there are photolithography method in which material for spacer is deposited on the lower panel on which cathode array and gate electrode are formed and it is patterned a method for scattering minute particles for spacer on the substrate, a method for manufacturing a spacer using individual process and arranging the spacer on the lower panel, or printing method.
However, the above described methods each have serious problems. The photolithography method has an advantage in manufacturing a minute spacer, but it has a complex process of patterning the spacer material after forming the photosensitive film on the material formed with spacer material and removing the photosensitive film pattern which is remained where there is a difficulty of selecting material for spacer. And the method for scattering minute particles for spacer on the substrate is difficult to manufacture panel of high density and can destroy cathode tips in case that the particles are scattered on the entire panel.
Also, in the case that the spacer is manufactured and arranged in individual process, it is difficult to arrange and fix the spacer to the correct position, and the printing method can apply and use the isolation wall formation method being used in the conventional PDP but it has a fault that a high spacer can not be formed with a narrow width. It is due to the fact that it becomes difficult to control the condition of process since the gap between the top portions of mask and printed page is changed and the print pressure is also changed as the stack print is executed over and over again, and becomes difficult to form a thick spacer since the accumulated print thickness for one print decreases gradually as the stack print is executed because the portion printed already is inserted to the following mask pattern hall.